Buggy code:
public class Game { public static void main ( String [ ] args ) { Bleach myGame = new Bleach ( ) ; myGame . loadImages ( "assets//images//assets.json" ) ; myGame . loadSounds ( "assets//sounds//assets.json" ) ; myGame . setFPS ( 60 ) ; myGame . setSize ( 800 , 600 ) ; myGame . setTitle ( "My<seq2seq4repair_space>super<seq2seq4repair_space>game!" ) ; Level firstLevel = new Level ( 2800 , 1200 , "Town" ) ; EntityBlob blobby = new EntityBlob ( myGame . getSprite ( "blob" ) , 200 , 264 ) ; Player player = new Player ( myGame . getSprite ( "mushi" ) , 100 , 100 ) ; firstLevel . addMobile ( blobby ) ; firstLevel . addPlayer ( player ) ; firstLevel . levelBuilder ( myGame . loadLevel ( "assets//levels//level1.json" ) ) ; myGame . addLevel ( firstLevel ) ; myGame . init ( ) ; Receptionist receptionist = new Receptionist ( ) { @ Override public void handleEvent ( ActionEvent event ) { } @ Override public void handleEvent ( MouseEvent event ) { } } ; receptionist . addKeyBinding ( new KeyBinding ( KeyStroke . getKeyStroke ( "pressed<seq2seq4repair_space>A" ) , "pressed<seq2seq4repair_space>A" , new AbstractAction ( ) { @ Override public void actionPerformed ( ActionEvent e ) { player . getForce ( ) . setVectorAngle ( Math . PI ) ; player . isMoving ( true ) ; System . out . println ( "Player<seq2seq4repair_space>moving<seq2seq4repair_space>to<seq2seq4repair_space>the<seq2seq4repair_space>left." ) ; } } ) ) ; receptionist . addKeyBinding ( new KeyBinding ( KeyStroke . getKeyStroke ( "released<seq2seq4repair_space>A" ) , "released<seq2seq4repair_space>A" , new AbstractAction ( ) { @ Override public void actionPerformed ( ActionEvent e ) { player . isMoving ( false ) ; } } ) ) ; receptionist . addKeyBinding ( new KeyBinding ( KeyStroke . getKeyStroke ( "pressed<seq2seq4repair_space>D" ) , "pressed<seq2seq4repair_space>D" , new AbstractAction ( ) { @ Override public void actionPerformed ( ActionEvent e ) { player . getForce ( ) . setVectorAngle ( 0 ) ; player . isMoving ( true ) ; System . out . println ( "Player<seq2seq4repair_space>moving<seq2seq4repair_space>to<seq2seq4repair_space>the<seq2seq4repair_space>right." ) ; } } ) ) ; receptionist . addKeyBinding ( new KeyBinding ( KeyStroke . getKeyStroke ( "released<seq2seq4repair_space>D" ) , "released<seq2seq4repair_space>D" , new AbstractAction ( ) { @ Override public void actionPerformed ( ActionEvent e ) { player . isMoving ( false ) ; } } ) ) ; receptionist . addKeyBinding ( new KeyBinding ( KeyStroke . getKeyStroke ( "released<seq2seq4repair_space>SPACE" ) , "released<seq2seq4repair_space>SPACE" , new AbstractAction ( ) { @ Override public void actionPerformed ( ActionEvent e ) { if ( player . isLanded ( ) ) { <START_BUG> player . addExternalForce ( new ExternalForce ( Math . toRadians ( 270 ) , 10 ) ) ; <END_BUG> player . setLanded ( false ) ; System . out . println ( "JUMP" ) ; } else System . out . println ( "NO<seq2seq4repair_space>JUMP" ) ; } } ) ) ; ( ( Entity ) ( player ) ) . setOnCollision ( new CollisionListener ( ) { @ Override public void onCollision ( Entity collidedWith ) { } } ) ; myGame . addReceptionist ( receptionist ) ; myGame . run ( ) ; } }

Fix:
player . addExternalForce ( new ExternalForce ( Math . toRadians ( 270 ) , 200 ) ) ;